개발

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*JavaScript
var a = 3;
var b = 2;
var max;

max = a > b ?  a : b;              - 가능
a > b ? max = a : max = b;     - 가능
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*Java
int a = 1;
int b = 2;
int max;

max = a > b ?  a : b;              - 가능
a > b ? max = a : max = b;     - 문법 오류 (x)

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http://hangaebal.blogspot.kr/2014/06/java-javascript-difference-between-java.html

Set provides uniqueness guarantee i.e.g you can not store duplicate elements on it, but it's not ordered.
List is an ordered Collection and also allowes duplicates.
Map is based on hashing and stores key and value in an Object called entry. It provides O(1) performance to get object, if you know keys, if there is no collision.

Another key difference between Set, List and Map are that Map doesn't implement Collection interface, while other two does.

Popular impelmentation of Set is HashSet, of List is ArrayList and LinkedList, and of Map are HashMap, Hashtable and ConcurrentHashMap.


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- Set : 중복이 불가해서 고유성은 보장되지만, 순서 유지 불가능
- List : 순서가 유지되고, 중복 가능
- Map : key와 value로 entry라 불리는 Object를 저장하고 찾는다. 키를 알고 있고, 충돌이 없다면, object를 얻는데 performance가 가장 좋다


- Set, List는 Collection 인터페이스를 구현했지만, Map은 아니다.

- 구현체 중 많이 쓰이는것
> Set : HashSet
> List : ArrayList, LinkedList
> Map : HashMap, Hashtable, ConcurrentHashMap.



출처 :
http://javarevisited.blogspot.kr/2011/11/collection-interview-questions-answers.html

http://hangaebal.blogspot.kr/2014/06/difference-between-set-list-and-map-in.html

 Node.js - Error connection lost the server closed the connection
Error: Connection lost: The server closed the connection.


var db_config = {
  host: 'localhost',
    user: 'root',
    password: '',
    database: 'example'
};

var connection;

function handleDisconnect() {
  connection = mysql.createConnection(db_config); // Recreate the connection, since
                                                  // the old one cannot be reused.

  connection.connect(function(err) {              // The server is either down
    if(err) {                                     // or restarting (takes a while sometimes).
      console.log('error when connecting to db:', err);
      setTimeout(handleDisconnect, 2000); // We introduce a delay before attempting to reconnect,
    }                                     // to avoid a hot loop, and to allow our node script to
  });                                     // process asynchronous requests in the meantime.
                                          // If you're also serving http, display a 503 error.
  connection.on('error', function(err) {
    console.log('db error', err);
    if(err.code === 'PROTOCOL_CONNECTION_LOST') { // Connection to the MySQL server is usually
      handleDisconnect();                         // lost due to either server restart, or a
    } else {                                      // connnection idle timeout (the wait_timeout
      throw err;                                  // server variable configures this)
    }
  });
}

handleDisconnect();



출처 :
http://stackoverflow.com/questions/20210522/nodejs-mysql-error-connection-lost-the-server-closed-the-connection

http://hangaebal.blogspot.kr/2014/06/nodejs-error-connection-lost-server.html